<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <form action="welcome.html">
        <input type="text" name="uname" class="nam">
        <input type="submit" value="提交" class="sub">
    </form>

    <script>
        var inp = document.querySelector('.nam');
        var sub = document.querySelector('.sub');
    </script>
</body>

</html>